The present invention relates to an optical recording medium such as a writable disc and readable disc, and more particularly to a method for recording information on a recording medium which has a light-transmissible substrate, a recording film made of organic coloring matter such as phthalocyanine coated on the substrate, and a reflection film covered on the recording film.
In a recording film of a writable optical recording medium, it is well known to use organic coloring matter such as cyanine.
As a method for writing information on the recording medium, a laser beam is focused on the recording film at a small area and converted into thermal energy so that the characteristic of the recording film is changed to form a pit. In order to properly change the characteristic of the recording film, two sheets of the recording mediums comprising a substrate and a recording film coated on the substrate is prepared. The recording films are disposed opposite to each other, interposing air therebetween, so called air sandwich construction.
A transparent substrate is irradiated with a laser beam for writing information and the pit is formed on the recording film. A laser beam for reading the recorded information has a rather weak power compared with the writing laser beam. The contrast between the pit and the area other than the pit is detected as an electric signal.
Besides the above mentioned recording medium, a recording medium on which information has been already recorded is provided. It is a read only memory (ROM) type recording medium which is widely used in the sound recording field and information processing field. In such a recording medium, it is not necessary to provide the writable recording film and prepits corresponding data to be reproduced are previously formed on a plastic substrate by press. A metallic reflection film made of Au, Ag, Cu, or Al is coated on the substrate and a protection film is covered on the reflection film. The most typical example thereof is a compact disc (CD). The format of writing and reading signal of the CD is standardized and the reproducing device of the CD is widely used as a CD player.
Since the writable recording medium uses a laser beam and is in the form of a disc, it is the same as the CD. Therefore, it has developed to adapt the recording medium to be played by the CD player.
In the conventional writable optical recording medium having the recording film of cyanine, a recording power of the laser beam must be properly determined in accordance with the characteristic of the recording medium, that is the characteristic of the reproduction signal which called .beta. value. More specifically, the recording power is determined so that the .beta. value becomes 0.04.
However, it has been found as a result of research that the .beta. value 0.04 is only effective to the recording film made of cyanine or a recording film having the same characteristic change as the cyanine film and is improper to a recording film made of phthalocyanine. If the recording film of phthalocyanine is irradiated with the laser beam of a recording power dependent on the .beta. value 0.04, disadvantages such as increase of the block error rate (BLER) occur.